The present invention relates to a laser light source device used for, for example, recording and reproducing a hologram, a hologram apparatus using the laser light source device, and a method for detecting laser light.
Hologram recording apparatuses for recording data using holography have been developed. In a typical hologram recording apparatus, modulated signal light (light in which data is superimposed) and unmodulated reference light are generated from laser light and are radiated onto a hologram-recording medium at the same position. Accordingly, the signal light and the reference light interfere with each other on the hologram-recording medium to form a diffraction grating (hologram) at the irradiation point, and thus data is recorded on the hologram-recording medium.
When the hologram-recording medium on which the data is already recorded is irradiated with the reference light, diffracted light (reproducing light) is generated by the diffraction grating formed in the recording process. The reproducing light includes the data superimposed on the signal light in the recording process. Therefore, the recorded signal can be reproduced by receiving the reproducing light with a light-receiving element.
In general, single-mode laser light sources having extremely high coherence are used as hologram recording/reproducing light sources, and gas lasers, second harmonic generation (SHG) lasers, etc., are used. A conventional laser diode does not have sufficient coherence because of a multimode type. However, a hologram recording/reproducing light source with high coherence can be obtained by forming an external cavity laser. Accordingly, external cavity lasers using compact, power-saving blue laser diodes can also be used as hologram light sources.
In addition, wavelength reproducibility is important in hologram recording. In particular, when wavelength division multiplexing in which the wavelength is varied is performed, the wavelength of the output light is adjusted to a desired wavelength. In that case, a tunable external cavity laser, for example, may be used.
A Littrow type, for example, may be used as the external cavity. In this external cavity, a laser beam emitted from a laser diode is collimated by a collimating lens, and is radiated onto a reflective diffraction grating. The beam reflected by the diffraction grating is divided into zero-order light and first-order light. The first-order light returns to the laser diode along the optical path along which the laser beam has traveled from the laser diode to the diffraction grating. The returned laser beam serves to form a cavity including the reflective diffraction grating and the laser diode, and the laser diode oscillates at a wavelength determined by the pattern of the reflective diffraction grating and the distance between the reflective diffraction grating and the laser diode (see Japanese Unexamined Patent Application Publication No. 11-107377, paragraphs [0028] to and FIG. 1).
In the above-described tunable external cavity laser, the wavelength and intensity of laser light being output are detected. In addition, detecting means for detecting the wavelength and intensity that has a simple structure and that contributes to size reduction of the device is demanded.
In light of the above-described situation, it is desirable to provide a small laser light source device with a simple structure that can detect the wavelength and intensity of light, a hologram apparatus using the laser light source device, and a method for detecting laser light.